'We're not stupid people': Top US general would refuse an illegal order to use nuclear weapons

The top officer at US Strategic Command says an order from President Donald Trump or any of his successors to launch nuclear weapons can be refused if that order is determined to be illegal.

Air Force General John Hyten, commander of Strategic Command, told a panel at the Halifax International Security Forum yesterday that he and Mr Trump have had conversations about such a scenario and that he would tell Mr Trump he couldn't carry out an illegal strike.

Mr Trump's taunting tweets aimed at Pyongyang have sparked concerns primarily among congressional Democrats that he may be inciting a war with North Korea.

During testimony before the Foreign Relations Committee earlier this month, retired General Robert Kehler, who served as the head of Strategic Command from January 2011 to November 2013, also said the US armed forces are obligated to follow legal orders, not illegal ones.

Donald Trump's recent taunting of North Korea has increased concerns over a possible conflict between the countries. (AAP) ()

General Hyten said he's talked it over with Mr Trump.

"I think some people think we're stupid. We're not stupid people. We think about these things a lot. When you have this responsibility how do you not think about it?" he said.